This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. CD133 is a pentaspan membrane glycoprotein with homology to mouse Prominin. It was initially identified as a stem cell marker on a subset of CD34+ cells by the monoclonal antibody AC133. CD133 is over-expressed in glioblastoma, leukemia, prostate and colon cancers. The mechanism by which CD133 confers tumorigenesis is not understood. The open reading frame of human Prominin-1 predicted a protein of 865 amino acids with a molecular weight of 96.8 KD. The antibody, however, recognizes a 120KD single band on an SDS gel consistent with protein glycosylation. The CD133 transcript is expressed in a variety of tissues, with the highest expression being in kidney, pancreas and placenta. A single nucleotide deletion at position 1878 of human Prominin-1 which results in premature truncation of the protein, has been identified in human retinal degeneration, an autosomal recessive disorder (Maw, et. al. 2000). The localization of CD133 in the protrusions of plasma membrane suggests a role in cell polarity, migration, and interaction of stem cells with neighboring cells and/or extra-cellular matrix. Using Tandem Affinity Purification (TAP) and mass spectroscopy, we hope to identify binding partners of CD133 in order to understand signaling events downstream of CD133.